1. Field of the Invention
The present invention relates to a flat panel display device and a method of manufacturing the same, and, more particularly, to a flat panel display device manufactured according to a method using fewer masks and resulting in high brightness and simplified manufacturing.
2. Description of Related Art
In general, a flat panel display device includes a display panel and a driving circuit that drives the display panel. The display panel and the driving circuit are manufactured through different processes and then attached to each other. Thus, there is a problem in that the manufacturing process for each component is complicated, and the production cost for each is high.
In efforts to solve the problem, a technique is developed so that pixels and driving integrated circuits (ICs) are formed on a single substrate in such a way that the pixel is arranged on a display region of the substrate, and the driving ICs are arranged on a non-display region of the substrate. For example, in the case of an organic Electroluminescent (EL) display device, two thin film transistors (TFTs), a storage capacitor and an organic EL element are formed on the display region, and a CMOS transistor as a driving circuit element is formed on the non-display region.
FIG. 1 is a cross-sectional view illustrating a conventional flat panel display device having a CMOS transistor as a driving circuit element. A method of manufacturing the conventional flat panel display device is provided below with reference to FIG. 1.
First, a transparent insulating substrate 10 having a display region 11 and a non-display region 15 is provided. The display region 11 includes a first display region 12 on which a TFT used to drive the pixels is formed, and further includes a second display region 13 on which an organic EL element is formed. The non-display region 15 includes a first non-display region 16 on which an NMOS TFT is formed, and further includes a second non-display region 17 on which a PMOS TFT is formed.
A buffer layer is formed on the transparent insulating substrate 10. Then, first to third semiconductor layers 21 to 23 are formed on the buffer layer of the transparent insulating substrate 10 using a first mask. The first semiconductor layer 21 is arranged over the first non-display region 16, and the second semiconductor layer 22 is arranged over the second non-display region 17. The third semiconductor layer 23 is arranged over the first display region 12.
A gate insulating layer 40 is formed over the entire surface of the transparent insulating substrate 10. First to third gate electrodes 41 to 43 are formed on the gate insulating layer 40 using a second mask. The first gate electrode 41 is arranged over the first semiconductor layer 21, and the second gate electrode 42 is arranged over the second semiconductor layer 22. The third gate electrode 43 is arranged over the third semiconductor layer 22.
Using the first gate electrode 41 as a mask, an n-type low-density impurity is ion-implanted into the first semiconductor layer 21 to form first low-density source and drain regions 37 and 38.
Using a third mask, an n-type high-density impurity is ion-implanted into the first semiconductor layer 21 to form first high-density source and drain regions 31 and 32.
Hence, the first semiconductor layer 21 has a lightly doped drain (LDD) structure. However, when an ion-implanting process (used to form the first low-density source and drain regions 37 and 38) is omitted, the first semiconductor layer 21 has an offset structure.
Using a fourth mask that exposes the remaining portion except for the first non-display region 16, a p-type high-density impurity is ion-implanted into the second and the third semiconductor layers 22 and 23 to form second source and drain regions 33 and 34 and third source and drain regions 35 and 36, respectively.
At this point, the third source and drain regions 35 and 36 are formed by ion-implanting a p-type impurity so as to form a PMOS TFT as a TFT for driving pixels. However, in order to form an NMOS TFT as a TFT for driving pixels, during a third mask process, an n-type high-density impurity can be ion-implanted into the third semiconductor layer 23.
Subsequently, an interlayer insulating layer 50 is formed over the entire surface of the transparent insulating substrate 10. Then, using a fifth mask, the gate insulating layer 40 and the interlayer insulating layer 50 are simultaneously etched to form contact holes 51 to 56.
Thereafter, using a sixth mask, first to third source and drain electrodes 61 to 66 are formed. The first to the third source and drain electrodes 61 to 66 are electrically connected to the first to third source and drain regions 31 to 36 through the contact holes 51 to 56, respectively.
A passivation layer 70 is formed over the entire surface of the transparent insulating substrate 10. Using a seventh mask, the passivation layer 70 is etched to form via hole 71. The via hole 71 exposes a portion of either of the third source and drain electrodes 65 and 66. In FIG. 1, the via hole 71 exposes the third drain electrode 66.
Using an eighth mask, a pixel electrode 80 is formed over the second display region 13. The pixel electrode 80 serves as a lower electrode of the organic EL element and is made of a transparent conductive material. The pixel electrode 80 is also electrically connected to the third drain electrode 66 through the via hole 71.
A planarization layer 90 is formed over the entire surface of the transparent insulating substrate 10 and etched using a ninth mask to form an opening portion 91 that exposes a portion of the pixel electrode 80.
Even though not shown in FIG. 1, an organic EL layer is formed on the pixel electrode 80 to cover the opening portion 91. Also, an upper electrode is formed to cover the organic EL layer. Therefore, the conventional flat panel display device is completed.
However, since nine masks are required to manufacture the conventional flat panel display device as described above, the manufacturing process is quite complicated, thereby lowering a manufacturing yield. In addition, light emitting from the organic EL layer formed on the pixel electrode 80 has to pass through several layers, including the gate insulating layer 40, the interlayer insulating layer 50, and the passivation layer 70. Hence, most of the light emitting from the organic EL layer is lost due to multi-reflection. As a result, light transmittance is lowered as is the brightness of the panel.